# RefArray.modifyAt

Modify the value at a particular index of a RefArray.

## Signatures

```ts
export declare const modifyAt: {
    <A>(index: number, f: (a: A) => A): <E, R>(ref: RefArray<A, E, R>) => Effect.Effect<ReadonlyArray<A>, E, R>;
    <A, E, R>(ref: RefArray<A, E, R>, index: number, f: (a: A) => A): Effect.Effect<ReadonlyArray<A>, E, R>;
};
```

## Why

Keeps modify at atomic with respect to competing RefSubject writes instead of splitting the read
and replacement into separate effects.

## Ownership and lifetime

Running modify at performs one serialized array transition and resolves with its committed
value. It acquires no resource; failures and services remain those of the source ref.